Growing at that rate at this point in your company's lifecycle is pretty extraordinary. So not sure why you would consider them to be a cautionary tale.
As for what has happened to them. They have been on an acquisition binge the last few years e.g. Trello, StatusPage, OpsGenie, Mindville etc. And as mentioned above they have been rewriting their UI in a new React framework called Atlaskit.
I also used to think Atlassian was a pretty poorly run company but then you look into it and actually the opposite is true. Although they did let Github, Gitlab, Slack dominate them.
Next few years will be interesting as Gitlab is moving very fast into their space.
Slack is the new Sharepoint, everyone uses it but no one really wants to and it doesn't really fit the bill but everyone else is doing it so companies adopt it.
Microsoft Teams Chat UI is garbage. It uses a lot of space, i can't just have a list of channels, no i need groups etc.
It even doesn't matter to me if its slack or hipchat or matrix or whatever. I don't know why we migrated to slack.
I don't get why Teams doesn't provide a lightweight chat typical UI. I would just switch to Teams. After all video calls are much better on Teams and more stable.
But then Slack integrated Teams and Zoom. They clearly don't want to compete in this area and i also don't get why.
And yes, Atlassian did drop the ball. We'll see the fallout in five years, I don't see how they can save the company now.
I don't even think Jira is specifically bad. If someone was only using it for basic project managment and ticketing, it'd be acceptable.
However, occupies the same niche as SAP or Oracle businessware.
First, Take a service that must be ergonomic because people rely on it all day to do their job. Next, make the primary requirement the ability for managment and finance to run reports. Then, outsource it to a company that wants to add custom web frameworks on top of a decades old project. Finally, graft on decades of customizations done by different generations of contractors.
If you can admin your own Jira instance and keep the fields and plugins to exactly what you need, it's pretty nice. I keep going back to it for the customizable workflows and fine-grained access control.
Unfortunately, every corporate Jira instance I've ever worked with has been overrun with every possible field possible, an unnecessary and constantly shifting mishmash of plugins and horribly slow access. You're paying the price for all of that cruft that you don't need and which can't be removed because "maybe someone wants it."
I've seen multiple different fields for the same value, each of them created for their specific team. The instance is slow AF most of the time due to the bloat and often I can't even assign a sprint to a JIRA because the field doesn't load anymore.
My company had resisted the urge to bolt on additions more than most. We recently migrated from Cloud to on-prem Server as a result of being acquired, and it is amazing how much zippier our project is compared to some of the peer projects that have accumulated cruft.